1. Field of the Invention
The present invention relates to a controller and an image display device.
2. Related Background Art
For image display devices which change a gamma table in accordance with an input image, for example, the following techniques have been proposed.
Japanese Patent Application Laid-Open No. H06-178153 discloses a gamma correction method of preparing a plurality of gamma tables and selecting one gamma table from the plurality of gamma tables in accordance with a histogram distribution of an input image to correct the gamma value (background art 1). With this method, the gamma table is selected which gives a high contrast to an input image having a high gradation to convert the gradation data of the input image in accordance with the selected gamma table.
Japanese Patent Application Laid-Open No. 2001-343957 discloses a liquid crystal display apparatus wherein the total gradation of brightness of input image data is divided into a plurality of sections, a histogram representative of an occurrence frequency of brightness of the input image data contained in each section is detected, the gradation characteristics are converted so that the contrast of display data in a high occurrence frequency gradation section is emphasized and the contrast in a low occurrence frequency gradation section is suppressed, and a color image is displayed in accordance with the display data having the converted gradation characteristics (background art 2).
The above-described techniques correct the gradation/intensity characteristics of an input signal by converting the gradation data. As a gamma correction method of changing the waveform itself of a drive signal for a display element modulated in accordance with gradation data, Japanese Patent Application Laid-Open No. 2000-39868 discloses an LED display unit which has first intensity modulation means for performing pulse width modulation in accordance with the gradation data and second intensity modulation means for performing gamma correction by using a low pulse current value in an area where a pulse width is narrow and a high pulse current value in an area where a pulse width is wide (background art 3).
The above-described technique discloses of a pulse width modulation method of changing a pulse width in accordance with the gradation data. Japanese Patent Application Laid-Open No. H07-181917 discloses another modulation method using the gradation data. According to this method, signals in a column direction applied to pixels in a selected row are selected from a sequence Vi (N≧2, 0≦i≦N) of N+1 voltages increasing their amplitude precisely, and a column selection time is divided equally by S at a time interval of Δt. An image is displayed at each gradation level by selecting, as the signal applied to each column, (S−j) first voltages Vi and j second voltages Vi+1 (or Vi−1) at respective time intervals (background art 4).
Japanese Patent Application Laid-Open No. 2003-15582 discloses an image display apparatus using an electron source having electron emission elements which has a modulation signal generation unit for modulating the pulse width of a pulse signal for driving an electron emission element, and a voltage of the pulse signal is changed in accordance with whether an average intensity is equal to or higher than a predetermined value.